This invention relates to ultrasonic diagnostic imaging systems and, in particular, to ultrasonic diagnostic imaging systems in which image brightness and contrast is automatically controlled.
Ultrasound imaging is often used in the diagnosis of patients who complain of nonspecific abdominal pain To diagnose this symptom the clinician will image most or all of the major organs of the abdomen. This will produce twenty, thirty, or more images of different organs at different depths, and from different acoustic windows of the body. Consequently the ultrasonic echoes obtained by such scanning will have undergone varying levels of attenuation as the ultrasound beams and echoes traverse different paths through the body. The varying echo levels will result in images of differing brightness. When the clinician notices these varying image appearances, the first instinct is to adjust the ultrasound system controls to negate them. For instance, if the deepest portion of an image is unusually dark, the clinician will adjust the time gain compensation (TGC) setting to provide more gain in the image at greater depths. If the overall brightness of the image is too bright or too dark, the clinician will adjust the overall gain control dial. If the image is noisy, especially in fluid-filled regions such as the gall bladder, the clinician will adjust the dynamic range of the signal path or image processor. It would be desirable to alleviate this task of constant adjustment by providing an ultrasound system that will recognize these image variations and provide the needed compensation automatically, so that the variety of images acquired during a study will exhibit comparable image appearance.
In accordance with the principles of the present invention, an ultrasonic diagnostic imaging system is provided which automatically compensates for variations in brightness or contrast. In accordance with one aspect of the present invention, variations in brightness are compensated by computing offsets to a nominal TGC curve which will compensate for depth dependent attenuation, then applying the offsets to the TGC curve for subsequent images. In accordance with another aspect of the present invention, image dynamic range is analyzed by comparing measurements of a recent image to comparable measurements of a reference image, then adjusting the dynamic range of the image processing path in accordance with the noted differences. In accordance with still another aspect of the present invention, differences between the compression function used to reduce the dynamic range of a recent image and a reference image are used to automatically adjust overall system gain for substantially uniform image production by the ultrasound system.